A silicon carbide (SiC) substrate has an extremely small impurity thermal diffusion coefficient, and an impurity thermal diffusion process cannot be used for silicon carbide (SiC) substrates in practice. Therefore, to control the electrical conductivity of a SiC substrate, it is necessary to activate impurities by performing an annealing treatment at a temperature of 1500 to 2000 degrees centigrade after impurity ion implantation. Therefore, an electron bombardment heating technique is used as a technique for heating a substrate heat treatment apparatus that performs an activation annealing treatment in the above mentioned temperature range, so that each SiC substrate is rapidly heated, and excellent annealing characteristics are achieved as disclosed (see Patent Document 1, for example).
As a temperature control method for realizing rapid heating by an electron bombardment heating technique, there has also been a suggested method by which the temperature is increased up to a preset temperature while the emission current value is maintained at a fixed value, and the temperature control is switched to PID control after the temperature reaches the preset temperature (see Patent Document 2, for example).